1. Field of the Invention
The present invention relates to a vehicle control apparatus that includes a power unit having an engine and a continuously variable transmission connected to the engine, and a power unit controller for switching the power characteristics of the power unit in accordance with the driving mode.
2. Description of the Related Art
A continuously variable transmission provided in a power transmission system of a vehicle includes a primary pulley mounted on an input shaft, a secondary pulley mounted on an output shaft, and a drive chain wrapped around these pulleys. In such a continuously variable transmission, any speed ratio can be set by regulating groove widths of the pulleys. Hence, the speed ratio can be switched in stages to perform speed shifting as in a manual transmission or an automatic transmission. As a result, also in the vehicle equipped with the continuously variable transmission, the same shift feel as that of a multi-stage transmission can be obtained, thereby enhancing marketability of the vehicle.
During speed shifting in such a multi-stage transmission mode, because the speed ratio is switched in stages, the shift speed is higher than that in a continuously variable transmission mode, in which the speed ratio is continuously changed. Accordingly, upon upshifting in the multi-stage transmission mode, an input side rotational speed is rapidly reduced to generate inertia torque due to inertia in the primary pulley or the like. The inertia torque acts in a direction to accelerate the primary pulley, thereby temporarily increasing output torque from the continuously variable transmission to cause shift shock.
In order to avoid the shift shock caused by the inertia torque, a technique has been developed. The technique includes reducing engine torque during an upshift, thereby allowing the inertia torque during the upshift to be absorbed. However, in a coasting state in which the engine torque is very small, it is difficult to reduce the engine torque by an amount equivalent to that of the inertia torque. Accordingly, another technique has been developed in which, in the case where a substantial reduction in the engine torque is difficult to achieve, the shift speed is reduced so as to reduce inertia torque, thereby avoiding shift shock (see, for example, Japanese Unexamined Patent Application Publication No. H11-20513).
There has been developed a vehicle in which the throttle characteristics of an engine or the shift characteristics of a continuously variable transmission are switched in accordance with the driving mode, such as a fuel-efficient mode or a high-power mode, to switch the power characteristics of a power unit. In such a vehicle in which the power characteristics are switched in accordance with the driving mode, a range of reduction in shift speed, which is reduced so as to reduce the foregoing inertia torque, also needs to be set in accordance with the driving mode so that a driver does not feel uncomfortable. That is, in order to match the range of reduction in the shift speed with the power characteristics in each driving mode, the range of reduction in the shift speed needs to be preset by experimentation or simulation. However, setting of the range of reduction in the shift speed corresponding to each driving mode involves complicated matching work which results in increased development costs of the vehicle.